Quartz glass or ceramic is suitably used for a transparent portion of an arc tube of a discharge lamp, so that the arc tube may efficiently transmit light generated in an electrical discharge space of the discharge lamp, and so as to withstand a high temperature due to an electric discharge arc. The translucent ceramic becomes an indispensable component as a composition material of the arc tube when the above-mentioned quartz glass cannot be used because of the property of gas to be enclosed in the electrical discharge space. Of course, in some cases, for example, where the quartz glass becomes clouded depending on an operating temperature of a lamp, the ceramic arc tube is suitably chosen and used based on the kind of the lamp and the use thereof. Examples of such lamps are disclosed in Japanese Patent Application Publication No. H08-236084 (an excimer lamp), Japanese Patent Application Publication No. H08-329896 (a metal halide lamp), and Japanese Patent Application Publication No. 2006-318656 (a flash lamp) etc.
The ceramic material of a transparent portion of such a ceramic arc tube is YAG or single crystal sapphire. Sealing members are in an approximately disk-like lid shape, and are airtightly attached to each end portion of a cylindrical pipe with a silver soldering. Steps of a sealing process will be described below, referring to FIGS. 9A through 9C, which are explanatory diagrams of the steps of the sealing process. (1) Paste-like material 92 for forming a metallized layer is coated on an end portion of a tubular ceramic member 91 (FIG. 9A). (2) The ceramic member 91 is heated at 1400° C. or more, and the metallized layer is calcinated. (3) Paste-like brazing material 93 is coated on the calcinated metallized layer 92′ (FIG. 9B). (4) A lid portion material 94 is put on the ceramic member 91, and they are put in a baking furnace for calcination (FIG. 9C). (5) Air is discharged from the inside of the pipe by using an exhaust pipe formed on the lid portion material 94, and after the gas for electric discharge is enclosed, the exhaust pipe is sealed. In addition, in FIG. 9C, a reference number 93′ indicates a brazing material which is fixed thereto after it is melted by the calcination.
Thus, in a manufacture method of a discharge lamp, it is necessary to perform metallizing processing to at least part of an end portion(s) of the ceramic member 91 where the brazing material 93 (93′) is formed. This is because it relates to the wetness of the brazing material, that is, it is necessary to form a metal layer as a base for the brazing on the ceramic surface, since the wetness of the brazing material is lower than that of ceramic.
However, the metallizing processing, which is indispensable to the brazing, requires a treatment at a high temperature of 1400° C. or more in non-oxidizing atmosphere. Therefore, although this is a pre-processing prior to the brazing of such a discharge lamp, there is a problem that time is required therefore and energy cost thereof is high. In addition, in the metallizing processing, it is necessary to put the arc tube composition material in a hot kiln and leave it for a fixed time. At this time, substances, such as metal, may float from components of the metallizing layer, and baking may occur inside the arc tube due to the high temperature. Therefore, when a very small quantity of substance, which enters and is mixed into the arc tube, is exposed to electric discharge, an expected lamp performance may not be demonstrated.